What is the difference between the main metadata.db and sub-directory metadata.db files?

There is only one metadata.db file and that is in the root of your calibre library. The other files you see are metadata.opf files.

Quote:

Originally Posted by iridius

If I have a library but have lost teh metadata.db file in the root, will the metadata.db files in the subdirectories for each book do anything?

Those other metadata files are all opf files and yes these files could be used to rebuild your metadata.db (calibre database) by using the Restore database menu option under Library maintenance (see attached).

Those other metadata files are all opf files and yes these files could be used to rebuild your metadata.db (calibre database) by using the Restore database menu option under Library maintenance (see attached).

The reconstructed metadata.db file should have all the original book related info. It won't have an non-book related info. My primary concern about non-book related info that will be missing is custom recipes. I have many of them.

Custom columns are also stored there and won't get recovered. I run a separate backup solely on the metadata.db file, in conjunction with a full backup of all books and the metadata.db file.

Personally, I'd never use the Restore database menu option as it wouldn't give me what I want most - recipes. I'd simply use my best backed up metadata.db (with my recipes) and then run an error analysis on the db to find books that are in the folders, but not in the db.

Great! Is there anything other than custom recipes that doesn't get restored? I don't think I'm ready to give up my metadata.db backups yet, but it would be nice to know that I could get back even if I'd lost my backups by running restore and grabbing my original recipe mods (which I usually keep in my recipe development area).